Related Experiment Videos
Negative functional effects of cGMP mediated by cGMP protein kinase are reduced in T4 cardiac myocytes
1Heart and Brain Circulation Laboratory, Department of Physiology and Biophysics and Surgery, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, One Robert Wood Johnson Place, CN-19, New Brunswick, NJ 08903-0019, USA.
Abstract:
We tested the hypothesis that in isolated rabbit cardiac myocytes, the negative functional effects of cyclic GMP are partly mediated by cyclic GMP-dependent protein kinase activity, and that these effects are altered in thyroxine (T4, 0.5 mg/kg/day for 16 days)-induced hypertrophic myocytes. Using isolated ventricular myocytes from control (N=8) and T4 (N=8) hypertrophic hearts, data for percent cell shortening (%) and maximum rate of contraction (microm/s) were collected using a video edge detector at baseline, after the addition of 10(-6) M 8-bromo-cyclic GMP (8-Br-cGMP), 10(-5) M 8-Br-cGMP, and 10(-6) M KT5823 (10-methoxy-10-methoxycarbonyl-9, 10, 11, 12-tetrahydro-9, 12-epoxy-(1H)-diinidolo [1, 2, 3, f-g: 3', 2', 1'-k-j]-pyrrolidino-[3,4-i] [1,6]-benzodiazocin-2-methyl-1-one, cyclic GMP protein kinase inhibitor). Protein phosphorylation was determined autoradiographically after gel electrophoresis. In both control and T(4) myocytes, 8-Br-cGMP caused a significant decrease in percent shortening (5.56+/-0.49% to 3.02+/-0.47% in control and 4.34+/-0.33% to 3.13+/-0.17% in T4 myocytes) and maximal rate of contraction 57.35+/-6.05 to 36.82+/-3.17 microm/s in control and 58.49+/-3.28 to 42.88+/-2.29 microm/s in T4 myocytes). KT5823 significantly increased percent shortening to 3.77+/-0.28% and rate to 48.68+/-4.71 microm/s after 8-Br-cGMP only in control myocytes. In T4 myocytes, the changes in percent shortening and rate after KT5823 were not significant. Protein phosphorylation was increased by 8-Br-cGMP in control and to a lesser extent in T4 myocytes, but the increment was reduced by KT-5823 in control only. These data demonstrated that cyclic GMP had negative functional effects partially mediated by cyclic GMP protein kinase in control myocytes. Cyclic GMP also exerted negative functional effects in thyroxine-induced hypertrophic myocytes, but cyclic GMP protein kinase activity was not an important regulator of these effects in T4 ventricular myocytes.
Insights
Cyclic GMP negatively impacts heart cell function, partly via cyclic GMP-dependent protein kinase in normal rabbit hearts. This pathway is less significant in thyroxine-induced hypertrophic myocytes.
Area of Science:
- Cardiovascular Physiology
- Molecular Cardiology
Background:
- Cyclic guanosine monophosphate (cGMP) plays a role in cardiac function.
- Thyroxine-induced cardiac hypertrophy alters myocyte responsiveness.
Purpose of the Study:
- To investigate the role of cGMP-dependent protein kinase (PKG) in mediating the functional effects of cGMP in rabbit cardiac myocytes.
- To determine if these cGMP-mediated effects are altered in thyroxine-induced hypertrophic myocytes.
Main Methods:
- Isolated ventricular myocytes from control and thyroxine-treated rabbits were used.
- Cell shortening and contraction rate were measured using a video edge detector.
- Effects of 8-bromo-cGMP and the PKG inhibitor KT5823 were assessed.
- Protein phosphorylation was analyzed via autoradiography.
Main Results:
- 8-bromo-cGMP significantly decreased cell shortening and contraction rate in both control and thyroxine-treated myocytes.
- KT5823 partially reversed the effects of 8-bromo-cGMP in control myocytes but not in thyroxine-treated myocytes.
- 8-bromo-cGMP increased protein phosphorylation in both groups, with a greater effect in control myocytes.
- KT5823 reduced 8-bromo-cGMP-induced phosphorylation in control myocytes only.
Conclusions:
- cGMP exerts negative functional effects on cardiac myocytes, partly mediated by PKG in normal rabbit hearts.
- While cGMP also negatively affects thyroxine-induced hypertrophic myocytes, PKG activity is not a significant regulator of these effects.